#include<iostream>
#include<cmath>
using namespace std;
int main()
{
	float x1, y1, x2, y2;
	while (cin >> x1 >> y1 >> x2 >> y2)
	{
		double ans = (x1 - x2) * (x1 - x2) + (y1 - y2) * (y1 - y2);
		printf("%.2lf\n", sqrt(ans));
	}
	return 0;
}